1. Field of the Invention
The present invention relates to a touch panel, and in particular to a method for detecting a touched position on a projected capacitive static capacitance type touch panel.
2. Description of the Related Art
In recent years, touch panels have become popular to be used as a user interface of a mobile device.
As one type of a touch panel, a static capacitance type is available. This type has come to be used in a wider market as being superior in transmittance and durability, though having a noise problem to be addressed. A touch panel, as being adhesively attached to a display screen, is likely affected by noise due to a display driving circuit. Accordingly, problems may be caused due to noise, including erroneous detection of a touch when the touch panel is not touched at all, difference between a calculated touched position and an actual touched position, and so forth.
As an example of a technique for reducing noise influence on a static capacitance type touch panel, Japanese Patent Laid-open Publication No. 2007-26065 discloses a touch detection method. According to this touch detection method, presence of a touch is determined when a measured value by a touch detection sensor is maintained equal to or larger than a predetermined threshold for a period longer than a predetermined period. This can avoid erroneous touch detection due to noise which appears only for a short period.
However, the method disclosed in the above described Japanese Patent Laid-open Publication No. 2007-26065 has some problems. First, as elapse of a predetermined period of time after a touch begins is needed to detect a touch, detection of a quick touch by a user (instantaneous touch, or the like) may be failed. Second, there is a possibility that a calculated position be different from an actual touched position as noise influence is not taken into consideration in a touched position calculation process following touch detection.